Radical ion salts

ABSTRACT

Novel radical ion salts of the formula ##STR1## wherein R 1 , R 2 , R 3  and R 4  independently of one another are each hydrogen, methyl, ethyl, phenyl, methoxy, ethoxy, fluorine, chlorine or bromine, or R 1  or R 1  and R 3  may furthermore be tert-butyl and/or R 1  and R 2  and/or R 3  and R 4  together may in each case form a radical of the formula ##STR2## where z is 0, 1, 2 or 3, and the fused aromatic rings are unsubstituted or monosubstituted or disubstituted by chlorine, bromine, methyl and/or methoxy, M m ⊕ is an m-valent alkali metal, alkaline earth metal, transition metal, tin, lead, thallium, ammonium, phosphonium, arsonium or stibonium ion, k is from 1 to 5, l is from 0.1 to 4, m is from 1 to 3, n is from 0.1 to 4, x is from 0 to 2 and y is from 0 to 6, and k, l, n, x and y may furthermore be non-integral numbers and (l+x)=n.m, are electrically conductive in the crystalline state. A number of the salts are stable at 300° C. and above. 
     The salts (I) are useful as electrical semiconductors and photoconductors, as electrode or storage material, in electric batteries, etc.

This application is a continuation of application Ser. No. 876,399,filed on June 20, 1986, now abandoned.

The present invention relates to novel radical ion salts based onN,N-dicyanoquinonediimines.

Radical ion salts of tetracyanoquinodimethanes and copper or silver areknown [Appl. Phys. Lett. 34 (1979), 405, J. Amer. Chem. Soc. 102 (1980),3659 and Chem. Skripta 17 (1981), 219].

The present invention relates to novel radical ion salts ofbiscyanimines of the formula ##STR3## where R¹, R², R³ and R⁴independently of one another are each hydrogen, methyl, ethyl, phenyl,methoxy, ethoxy, fluorine, chlorine or bromine and R¹ or R¹ and R³ mayfurthermore be tert-butyl or R¹ and R² and/or R³ and R⁴ together may ineach case form a radical of the formula ##STR4## where z is 0, 1, 2 or 3and the fused, aromatic rings are unsubstituted or monosubstituted ordisubstituted by chlorine, bromine, methyl and/or methoxy, M^(m)⊕ is anm-valent alkali metal, alkaline earth metal, transition metal, tin,lead, thallium, ammonium, phosphonium, arsonium or stibonium ion, k isfrom 1 to 5, l is from 0.1 to 4, m is from 1 to 3, n is from 0.1 to 4, xis from 0 to 2 and y is from 0 to 6, and k, l, n, x and y mayfurthermore be non-integral numbers and (l+x)=n.m.

In the microcrystalline state, the novel salts (I) (complexes) have ahigh electrical conductivity, which as a rule is clearly orsubstantially higher in single crystals. For example, the conductivitiesof the salts (I) are substantially superior to those of the knownradical ion salts based on tetracyanoquinodimethane and copper orsilver. Thus, the prior art TCNQ.Cu salt has a conductivity of 0.005S.cm⁻¹ [L. R. Melby et al., J. Amer. Chem. Soc. 84 (1962), 3374], whilethe corresponding radical ion salt according to the invention (Example37) has a conductivity of 0.02 S.cm⁻¹. A number of the compounds (I) arethermally stable at about 300° C. or above. Accordingly, the novelcomplexes are useful, for example, as electrical semiconductors andphotoconductors, for the antistatic treatment of plastics, as electrodeand storage material in electric batteries, for the production of solarcells, in fuel cells, for the conversion of radiation and for theproduction of electronic components. Microcrystalline films of the novelradical ion salts can be used for the production of bistable electricalswitching elements.

Specific examples for combinations of R¹, R², R³ and R⁴ are as follows:

(a) R¹, R², R³ and R⁴ are identical and are each hydrogen, fluorine,chlorine, methyl or methoxy or

(b) R¹ is chlorine, bromine, methyl, ethyl, methoxy, ethoxy, phenyl ortert-butyl and R², R³ and R⁴ are each hydrogen, or

(c) R¹ and R⁴ are identical and are each chlorine, methyl or methoxy andR² and R³ are each hydrogen, or

(d) R¹ and R² are identical and are each chlorine, methyl, methoxy orphenyl and R³ and R⁴ are each hydrogen, or

(e) R¹ and R³ are identical and are each chlorine, bromine, methyl,ethyl, methoxy, phenyl or tert-butyl and R² and R⁴ are each hydrogen or

(f) R¹, R² and R³ are each methyl and R⁴ is hydrogen, or

(g) R¹ is methyl, R³ is chlorine or bromine and R² and R⁴ are eachhydrogen, or

(h) R¹ and R² together form a radical of the formula ##STR5## where z is0, 1, 2 or 3 and the fused aromatic ring is unsubstituted ormonosubstituted or disubstituted by chlorine, methyl and/or methoxy, andR³ and R⁴ independently of one another are each hydrogen, chlorine ormethyl or

(i) R¹ and R², and R³ and R⁴, in each case together form a radical ofthe formula ##STR6## where z is 0, 1, 2 or 3 and the fused aromaticrings are unsubstituted or monosubstituted or disubstituted by chlorine,methyl and/or methoxy.

Suitable ions M^(m)⊕ are ions of metals whose redox potential is lessthan or equal to that of silver, eg. ammonium, phosphonium, arsonium andstibonium.

Examples of metal ions are those of the alkali metals, such as lithium,sodium, potassium, rubidium and cesium, those of the alkaline earthmetals, such as calcium, strontium and barium, those of the transitionmetals, such as chromium, manganese, iron, cobalt, nickel, copper, zinc,silver, cadmium and mercury, and those of tin, lead and thallium.

Examples of ammonium M^(m)⊕ are tetra-C₁ -C₄ -alkylammonium,tetraphenyl-C₁ -C₃ -alkylammonium, phenyl-C₁ -C₃ -alkyl-tris-C₁ -C₄-alkylammonium, C₁ -C₄ -alkylpyridinium, N-phenyl-C₁ -C₃-alkylpyridinium, quinolinium, N-C₁ -C₄ -alkylquinolinium, N-phenyl-C₁-C₃ -alkylquinolinium and the corresponding isoquinolinium compounds,phenazinium, N-C₁ -C₄ -alkylphenazinium and N-phenyl-C₁ -C₃-alkylphenazinium.

Particularly suitable phosphonium, arsonium and stibonium ions are thosewhich are derived from the triphenyl compounds.

Specific examples of M^(m)⊕ are Li.sup.⊕, Na.sup.⊕, K.sup.⊕, Rb.sup.⊕,Cs.sup.⊕, Mg²⊕, Ca²⊕, Ba²⊕, Sr²⊕, Cr³⊕, Mn²⊕, Fe²⊕, Fe³⊕, Co²⊕, Ni²⊕,Cu.sup.⊕, Cu²⊕, Zn²⊕, Ag.sup.⊕, Cd²⊕, Sn²⊕, Pb²⊕, Pb⁴⊕, Tl.sup.⊕, Tl³⊕,triphenylmethylphosphonium, triphenylmethylarsonium,triphenylmethylstibonium, tetramethylammonium, tetraethylammonium,tetrapropylammonium, tetrabutylammonium, tetrabenzylammonium,tetra(2-phenylethyl)ammonium, trimethylbenzylammonium,triethylbenzylammonium, pyridinium, N-methyl- and N-ethylpyridinium,N-methyl-2-methylpyridinium, N-methyl-3-methylpyridinium,N-methyl-4-methylpyridinium, N-benzylpyridinium, quinolinium, N-methyl,N-ethyl- and N-benzylquinolinium, phenazinium and N-methyl-, N-ethyl-and N-benzylphenazinium.

Preferred M^(m)⊕ ions are copper(I) and silver(I) ions,tetramethylammonium, tetraethylammonium, tetrabenzylammonium,trimethylbenzylammonium, triethylbenzylammonium, quinolinium,pyridinium, N-methylpyridinium, N-ethylquinolinium, N-methylquinolinium,phenazinium and N-methylphenazinium, of which copper (I), silver(I),pyridinium, N-methylpyridinium, quinolinium, N-methylquinolinium,phenazinium and N-methylphenazinium are particularly preferred.

The radical ion salts (I) according to the invention can be prepared byvarious processes. One route is the reaction ofN,N'-dicyanoquinonediimines of the formula (II) ##STR7## where R¹, R²,R³ and R⁴ have the above meanings, with halides, preferably iodides, ofthe above cations M^(m)⊕ in a molar ratio of from 1:0.5 to 1:3, in asolvent, if necessary at elevated temperatures. Examples of suitablesolvents are dichloromethane, chloroform, tetrahydrofuran,1,1,1-trichloroethane, acetonitrile, benzene, toluene, chlorobenzene anddichlorobenzene. The radical ion salts are isolated in a conventionalmanner by filtration under suction.

The novel radical ion salts (I) may furthermore be prepared by reactingan N,N'-dicyanoquinonediimine of the formula (II) with a metal M,preferably in powdered form, in a molar ratio of from 1:1 to 1:0.2, inone of the abovementioned solvents which is inert to the metal, ifnecessary at elevated temperatures. The radical ion salts are isolatedin a conventional manner by filtration under suction.

The novel radical ion salts (I) may furthermore be prepared byelectrolysis of a solution which contains an N,N'-dicyanoquinonediimineof the formula (II) and a salt containing one of the above cations(M^(m)⊕) in one of the above solvents, at from room temperature to -30°C. The temperature depends on the solubility of theN,N'-dicyanoquinoneimine. Preferably, electrolysis is carried out at <0°C., in particular from -10° to -30° C., in order as far as possible toavoid any decomposition which may occur. In this case too, the radicalion salts are isolated in a conventional manner by filtration undersuction. The yield of the radical ion salt (I) depends on the durationof electrolysis and on the solubility of (I) in the solvent used for theelectrolysis, since isolation of the dissolved salt (I) from theelectrolysis solution containing the conductive salt is very difficult.

The radical ion salts (I) according to the invention can also beprepared by reacting the lithium salt of an N,N'-dicyanoquinonediimineof the formula (II) with a salt containing one of the above cations(M^(m)⊕) in a solvent such as methanol, ethanol, propanol, water,acetonitrile or a mixture of these.

Microcrystalline films which consist of the novel radical ion salts canbe produced in a conventional manner by immersing a metallic body in asolution of an N,N'-dicyanoquinoneimine in one of the above solvents,preferably at elevated temperatures.

The Examples which follow illustrate the invention. Percentages for theyields are based on the theoretical yield. The stated conductivities aredetermined for powder pellets or single crystals.

EXAMPLE 1

A solution of 156 mg (100 millimoles) ofN,N'-dicyano-1,4-benzoquinonediimine is added dropwise to a filteredsolution of 1.34 g (10.0 ml) of lithium iodide in acetonitrile, whilestirring. Stirring is continued for 10 minutes, after which the productis filtered off under suction and washed with acetonitrile to give 98 mg(52%) of the corresponding radical ion salt in the form of a pale violetpowder which decomposes above 234° C.

Analysis: C₈ H₆ I₀.06 Li₁.06 N₄ O. Calculated: C 50.81, H 3.20, I 4.03,N 29.64%. Found: C 51.43, H 3.19, I 3.93, N 28.98%.

EXAMPLES 2 TO 9

A solution of copper(I) iodide in acetonitrile is added to a solution ofN,N'-dicyanoquinonediimine (II) in acetonitrile. During this procedure,a dark precipitate separates out and is filtered off under suction andwashed with acetonitrile. The N,N'-dicyanoquinonediimines (II) used arecharacterized by the substituents in columns 2 to 5 of Table 1.

The radical anion salts obtained are of the general formula (Ia)##STR8##

The meanings of k, l, n, x and y are given in columns 6 to 10 inTable 1. In the Table, the salts (Ia) are characterized by thedecomposition point and elemental analysis.

                                      TABLE 1                                     __________________________________________________________________________                                   Elemental analysis                                                                           Decomposi-                                                                          Yield                                                                             Conducti-             Ex-                            C  H   N  Other                                                                              tion point                                                                          [% of                                                                             vity                  ample                                                                             R.sup.1                                                                           R.sup.2                                                                           R.sup.3                                                                           R.sup.4                                                                         k  l  n x  y [%]                                                                              [%] [%]                                                                              elements                                                                           [°C.]                                                                        therory]                                                                          σ[S                                                                     ·                                                                    cm.sup.-1             __________________________________________________________________________                                                            ]                     2   H   H   H   H 1  1  1 0  0 44.20                                                                            1.63                                                                              25.04                                                                            Cu: 28.2                                                                           from 265                                                                            75                        3   CH.sub.3                                                                          H   H   H 1  1  1 0  0 45.81                                                                            2.69                                                                              23.45                                                                            Cu: 25.2                                                                           from 205                                                                            60                        4   CH.sub.3                                                                          CH.sub.3                                                                          H   H 1.3                                                                              1  1 0  0 51.47                                                                            3.59                                                                              23.83   from 205                                                                            51                        5   CH.sub.3                                                                          H   CH.sub.3                                                                          H 2  1  1 0  0 55.91                                                                            3.61                                                                              26.07   from 229                                                                            87                        6   OCH.sub.3                                                                         H   OCH.sub.3                                                                         H 3  2  2 0  0 46.78                                                                            3.09                                                                              21.96   from 280                                                                            78                        7   Cl  H   Cl  H 1.63                                                                             1  1 0  0 36.44                                                                            0.67                                                                              21.25   >350  46  2.5                   8   CH.sub.3                                                                          CH.sub.3                                                                          CH.sub.3                                                                          H 1.75                                                                             0.91                                                                             1 0.09                                                                             0 54.91                                                                            4.19                                                                              23.27                                                                            I: 2.81                                                                            from 173                                                                            83                        9   --(CH═CH).sub.2 --                                                                H   H 1.10                                                                             0.4                                                                              2 1.6                                                                              0 28.26                                                                            0.92                                                                              11.21                                                                            I: 36.78                                                                           >350  54  1.3 ·                                                                10.sup.-2             10  Cl  H   CH.sub.3                                                                          H 2  1  1 0  0 42.47                                                                            1.81                                                                              21.42   >350  98  0.4                   11  --(CH═CH).sub.2 --                                                                H   H 5  4  4 0  0 55.23                                                                            3.82                                                                              21.40   >350  78                        __________________________________________________________________________

EXAMPLE 12

The procedure described in Example 1 is followed, except that a solutionof copper(I) bromide in tetrahydrofuran is used, and a solution of2-chloro-5-methyl-N,N'-dicyano-1,4-benzoquinonediimine is added dropwiseto this. The corresponding radical ion salt of the formula ##STR9## isobtained in a yield of 93%. Mp.>350° C.

C₉ H₅ N₄ ClCu. Calculated: C 45.73, H 2.13, N 23.70%. Found: C 45.40, H1.85, N 23.42%.

Conductivity: 0.4 S.cm⁻¹ (powder).

EXAMPLES 13 TO 15

N,N'-Dicyanoquinonediimines (II) are stirred with silver powder inacetonitrile at room temperature. Insoluble material is filtered offunder suction. The N,N'-dicyanoquinonediimines (II) used arecharacterized by R¹ to R⁴ in columns 2 to 5 of Table 2.

The radical ion salts obtained are of the general formula (Ib) ##STR10##

The meanings of k, n and y are given in columns 6 to 9.

In Table 2, the salts (Ib) are characterized by the decomposition point,elemental analysis and the electrical conductivity.

                                      TABLE 2                                     __________________________________________________________________________                      Elemental analysis                                                                      Decomposi-                                                          C  H   N  tion point                                                                          Conductivity                                Example                                                                            R.sup.1                                                                         R.sup.2                                                                         R.sup.3                                                                         R.sup.4                                                                         k  n [%]                                                                              [%] [%]                                                                              [°C.]                                                                        σ[Scm.sup.-1 ]                        __________________________________________________________________________    13   H H H H 1  1 36.41                                                                            1.32                                                                              20.86                                                                            >350  1.7 19  10.sup.-2                           14   Cl                                                                              H Cl                                                                              H 1.1                                                                              1 30.05                                                                            0.36                                                                              16.93                                                                            >350  19.8                                        15   H H Cl                                                                              H 1.62                                                                             1 32.95                                                                            0.69                                                                              19.22                                                                            >350  8 · 10.sup.-2                      __________________________________________________________________________

EXAMPLE 16

Electrolysis is carried out in a cell which holds 60 ml of liquid and isdivided into 3 compartments by two G4 glass frits. Each compartment canbe filled or emptied under protective gas, independently of one another.

The electrodes are present in the outer compartments. Dividing the cellinto three parts prevents byproducts formed at the anode frompenetrating into the cathode space.

Two platinum sheets measuring 20×10×1 mm are used as the electrodes. Theelectrodes and the cell are cleaned with a mixture of 35% strengthhydrogen peroxide and concentrated sulfuric acid each time before beingused. They are then washed with water, after which the cell is steepedin distilled water for 1 day in order to remove final traces of acid.The cell is then dried at 120° C.

Current is supplied by a constant current source which can be regulatedbetween 0 and 250 μA.

By adjusting the cell temperature in a heatable bath, electrolysis canbe effected at defined temperatures.

To carry out the electrolysis, a solution of 92 mg (500 μmol) ofN,N'-dicyano-2,5-dimethyl-1,4-benzoquinonediimine and 170 mg (=1.00millimole) of silver nitrate in 60 ml of acetonitrile is introduced intoall three compartments of the cell, and electrolysis is effected at roomtemperature, using a current of 3 μA. Thin acicular crystals up to 3 cmlong grow at the cathode. After 80 hours, 12 mg (10%) of silver salt areisolated in the form of deep black needles of melting point 205° C.(decomposition).

Analysis (476.3): C₂₀ H₁₆ AgN₈. Calculated: C 50.43, H 3.39, N 23.53%.Found: C 50.42, H 3.29, N 22.91%.

Electrolysis of the solution is not taken to completion, in order toavoid excessive reduction.

EXAMPLE 17

A solution of 68 mg (=302 μmol) ofN,N'-dicyano-2,5-dichloro-1,4-benzoquinonediimine and 368 mg (2.27millimoles) of tetramethylammonium tetrafluoborate in acetonitrile issubjected to electrolysis at -25° C., using a current of 50 μA. After 40hours, the black needles up to 2 mm long which are deposited at thecathode and exhibit metallic gloss are collected, and washed withdiethyl ether. 20 mg (25%) of the radical salt of melting point 220° C.(decomposition) are obtained.

Analysis (476.3): C₂₂ H₁₆ AgN₉. Calculated: C 45.82, H 3.00, N 24.05%.Found: C 46.37, H 3.10, N 23.95%.

EXAMPLES 18 TO 36

The N,N'-dicyanoquinonediimines (II) characterized in Table 3 by R¹, R²,R³ and R⁴ are subjected to electrolysis together with salts containingcations M^(m)⊕, in acetonitrile, using procedures similar to thosedescribed in Examples 15 and 16. Electrolysis is carried out at betweenroom temperature (25° C.) and -20° to -25° C., depending on thesolubility of the N,N'-dicyanoquinonediimines (II) used. The yield of(I) is dependent on the duration of electrolysis and on the solubilityof the resulting compound (I) in acetonitrile. Isolation of thedissolved compound (I) from the acetonitrile solution formed duringelectrolysis and containing the conductive salt is very difficult.

Radical ion salts of the general formula (Ic) are obtained. ##STR11##

The meanings of k, M^(m)⊕ and n are given in Table 3 (columns 6 to 8).

The salts (Ic) obtained are characterized in columns 9 to 12 by theirdecomposition points and elemental analysis, and in some cases by theirconductivities.

                                      TABLE 3                                     __________________________________________________________________________                               Elemental analysis                                                                      Decomposi-                                                                          Yield                                                                             Conducti-                      Ex-                        C  H  N   tion point                                                                          [% of                                                                             vity                           ample                                                                             R.sup.1                                                                           R.sup.2                                                                           R.sup.3                                                                           R.sup.4                                                                         H.sup.m ⊕.sup.1                                                                k n [%]                                                                              [%]                                                                              [%] [°C.]                                                                        theory]                                                                           δ[S ·                                                          cm.sup.-1 ]                    __________________________________________________________________________    18  H   H   H   H Ag.sup.⊕                                                                       1 1 36.41                                                                            1.38                                                                             21.04                                                                             from 270                                                                            8                                  19  CH.sub.3                                                                          CH.sub.3                                                                          H   H Ag.sup.⊕                                                                       1 1 41.24                                                                            2.61                                                                             19.29                                                                             from 205                                                                            8                                  20  CH.sub.3                                                                          H   CH.sub.3                                                                          H Ag.sup.⊕                                                                       2 1 50.42                                                                            3.29                                                                             22.91                                                                             205   10  18                             21  CH.sub.3                                                                          H   Cl  H Ag.sup.⊕                                                                       2 1 41.41                                                                            1.88                                                                             21.41                                                                             from 207                                                                            38                                 22  Cl  H   Cl  H Ag.sup.⊕                                                                       1.7                                                                             1 33.25                                                                            0.20                                                                             19.70                                                                             from 305                                                                            24                                 23  Br  H   Br  H Ag.sup.⊕                                                                       3 2 25.03                                                                            1.06                                                                             14.35                                                                             > 350 15                                 24  Cl  H   Cl  H THA.sup.⊕                                                                      2 1 46.37                                                                            3.10                                                                             23.95                                                                             from 220                                                                            25  2 · 10.sup.-2         25  Br  H   Br  H THA.sup.⊕                                                                      3 2 35.82                                                                            2.89                                                                             17.43                                                                             from 205                                                                            6                                  26  Cl  H   Cl  H NHQ.sup.⊕                                                                      1.7                                                                             1 54.13                                                                            2.30                                                                             20.68                                                                             from 217                                                                            45  0.1                            27  Br  H   Br  H NHQ.sup.⊕                                                                      5 4 45.01                                                                            2.23                                                                             15.36                                                                             198   19                                 28  Br  H   Br  H NHQ.sup.⊕                                                                      3 2 42.67                                                                            2.02                                                                             16.09                                                                             from 218                                                                            43                                 29  Cl  H   Cl  H Q.sup.⊕                                                                        1 1 57.16                                                                            2.81                                                                             20.11                                                                             from 126                                                                            25                                 30  H   H   H   H NMP.sup.⊕                                                                      2 1 68.53                                                                            3.89                                                                             27.25                                                                             125   8                                  31  Cl  H   Cl  H NHP.sup.⊕                                                                      1 1 60.67                                                                            3.09                                                                             19.83                                                                             149   26                                 32  Br  H   Br  H NHP.sup.⊕                                                                      1 1 47.10                                                                            2.47                                                                             15.85                                                                             from 121                                                                            7                                   .sup.(1) TMA.sup.⊕  = tetramethylammonium, NMQ.sup.⊕ =                N--methylquinolinium, Q.sup.⊕ = quinolinium, NMP.sup.⊕ =              N--methylphenazinium                                                         33  CH.sub.3                                                                          H   Br  H Ag.sup.⊕                                                                       2 1 35.85                                                                            1.68                                                                             18.94                                                                             >350  45                                 34  --(CH.sub.2).sub.4 --                                                                 H   H Cu.sup.⊕                                                                       5 4 55.11                                                                            3.73                                                                             21.84                                                                             >350  58                                 35  Cl  H   Cl  H Cu.sup.⊕                                                                       1 1 32.59                                                                            0.73                                                                             18.83                                                                             >350  22  0.08.sup.(1)                   36  --(CH═CH).sub.2 --                                                                Cl  Cl                                                                              Ag.sup.⊕                                                                       1 1 36.89                                                                            1.02                                                                             14.21                                                                             >350  38  0.02.sup.(1)                   37  OCH.sub.3                                                                         H   OCH.sub.3                                                                         H Cu.sup.⊕                                                                       1 1 44.35                                                                            3.10                                                                             20.43                                                                             >350  22  0.7.sup.(1)                    38  H   H   H   H Cu.sup.⊕                                                                       1 1 43.24                                                                            1.85                                                                             25.59                                                                             >270  52  0.02.sup.(1)                   39  CH.sub.3                                                                          H   Cl  H Cu.sup.⊕                                                                       2 1 41.81                                                                            1.95                                                                             21.67                                                                             >350  46  300.sup.(2)                                                               0.4.sup.(1)                        40  CH.sub.3                                                                          H   Br  H Cu.sup.⊕                                                                       2 1 37.88                                                                            1.80                                                                             19.72                                                                             >350  86  0.3.sup.(1)                    __________________________________________________________________________     .sup.(1) measured on microcrystalline powder                                  .sup.(2) measured on the single crystal                                  

We claim:
 1. A radical ion salt of the formula: ##STR12## wherein R¹,R², R³ and R⁴ independently of one another are each hydrogen, methyl,ethyl, phenyl, methoxy, ethoxy, fluorine, chlorine or bromine; or R¹ orR¹ and R³ are each tert-butyl; or R¹ and R² or R³ and R⁴ or R¹ and R²and R³ and R⁴ together form a radical of the formula: ##STR13## whereinz is 0, 1, 2 or 3, and wherein the fused aromatic rings are substitutedby chlorine, bromine, methyl or methoxy, M^(m+) is a cation whose redoxpotential is less than or equal to that of silver and which is selectedfrom the group consisting of m-valent alkali metals, copper, silver andtetra-C₁ -C₄ -alkyl ammonium, tetraphenyl-C₁ -C₃ -alkyl ammonium,phenyl-C₁ -C₃ -alkyl-tris-C₁ -C₄ -alkyl ammonium, C₁ -C₄-alkylpyridinium, N-(phenyl-C₁ -C₃ -alkyl)-pyridinium, quinolinium, N-C₁-C₄ -alkylquinolinium, N-(phenyl-C₁ -C₃ -alkyl)-quinolinium,isoquinolinium, N-C₁ -C₄ -alkylisoquinolium, N-(phenyl-C₁ -C₃-alkyl)-isoquinolinium, phenazinium, N-C₁ -C₄ -alkylphenazinium orN-(phenyl-C₁ -C₃ -alkyl)-phenazinium; and wherein k is from 1 to 5, l isfrom 0.1 to 4, m is from 1 to 3, n is from 0.1 to 4, x is from 0 to 2and y is from 0 to 6, or k, l, n, x and y are non-integral numberswherein the number of negative charges on the radical (l⁻) plus thenumber of iodine anions (x) is equal to the number of metal cationsmultiplied by the number of positive charges per metal cation, therebyensuring that the radical ion salt is neutral.
 2. The radical ion saltas claimed in claim 1, wherein said substituted fused aromatic rings aremono- or di-substituted by chlorine, bromine, methyl or methoxy.
 3. Aradical ion salt of the formula: ##STR14## where R¹ and R³ are eachhydrogen, methyl, methoxy, chlorine or bromine; R² is hydrogen or methyland R⁴ is hydrogen; or R¹ and R² together are of the formula: ##STR15##and wherein M^(m+) is a copper or silver ion or pyridinium,N-methylpyridinium, quinolinium, N-methylquinolinium, phenazinium orN-methylphenazinium, k is from 1 to 5, l is from 0.1 to 4, m is from 1to 3, n is from 0.1 to 4, x is from 0 to 2, or k, l, n and x arenon-integral numbers and, wherein the number of negative charges on theradical ion (l⁻) plus the number of iodine anions (x) is equal to thenumber of metal cations multiplied by the number of positive charges permetal cation, thereby ensuring that the radical ion salt is neutral. 4.The radical ion salt as claimed in claim 1, wherein M^(m)⊕ is acopper(I) or silver ion or tetramethylammonium,tetraethylbenzylammonium, tetrabenzylammonium, trimethylbenzylammonium,triethylammonium, quinolinium, pyridinium, N-methylpyridinium,N-ethylquinolinium, N-methylquinolinium, phenazinium orN-methylphenazinium.
 5. The radical ion salt of the formula according toclaim 1, wherein M^(m)⊕ is a copper(I) or silver ion or pyridinium,N-methylpyridinium, quinolinium, N-methylquinolinium, phenazinium orN-methylphenazinium.
 6. The radical ion salt as claimed in claim 1,wherein R¹, R², R³ and R⁴ are each hydrogen, fluorine, chlorine, methylor methoxy or R¹ is chlorine, bromine, methyl, ethyl, methoxy, ethoxy,phenyl or tert-butyl and R², R³ and R⁴ are each hydrogen, or R¹ and R⁴are each chlorine, methyl or methoxy and R² and R³ are each hydrogen, orR¹ and R² are each chlorine, methyl, methoxy or phenyl and R³ and R⁴ areeach hydrogen, or R¹ and R³ are each chlorine, bromine, methyl, ethyl,methoxy, phenyl or tert-butyl and R² and R⁴ are each hydrogen, or R¹, R²and R³ are each methyl and R⁴ is hydrogen, or R¹ is methyl, R³ ischlorine or bromine and R² and R⁴ are each hydrogen, or R¹ and R²together form a radical of the formula: ##STR16## where z is 1 or 2, andthe fused benzene ring is unsubstituted or monosubstituted ordisubstituted by chlorine, methyl or methoxy, and R³ and R⁴independently of one another are each hydrogen, chlorine or methyl. 7.The radical ion salt as claimed in claim 1, wherein R¹, R², R³ and R⁴are each hydrogen, fluorine, chlorine, methyl or methoxy or R¹ ischlorine, bromine, methyl, ethyl, methoxy, ethoxy, phenyl or tert-butyland R², R³ and R⁴ are each hydrogen, or R¹ and R⁴ are each chlorine,methyl or methoxy and R² and R³ are each hydrogen, or R¹ and R² are eachchlorine, methyl, methoxy or phenyl and R³ and R⁴ are each hydrogen, orR¹ and R³ are each chlorine, bromine, methyl, ethyl, methoxy, phenyl ortert-butyl and R² and R⁴ are each hydrogen, or R¹, R² and R³ are eachmethyl and R⁴ is hydrogen, or R¹ is methyl, R³ is chlorine or bromineand R² and R⁴ are each hydrogen, or R¹ and R² together form a radical ofthe formula ##STR17## where z is 1 or 2, and the fused benzene ring isunsubstitued or monosubstituted or disubstituted by chlorine, methyl ormethoxy, and R³ and R⁴ independently of one another are each hydrogen,chlorine or methyl.
 8. The radical ion salt as claimed in claim 1,wherein R¹, R², R³ and R⁴ are each hydrogen, fluorine, chlorine, methylor methoxy, or R¹ is chlorine, bromine, methyl, ethyl, methoxy, ethoxy,phenyl or tert-butyl and R², R³ and R⁴ are each hydrogen, or R¹ and R⁴are each chlorine, methyl or methoxy and R² and R³ are each hydrogen, orR¹ and R² are each chlorine, methyl, methoxy or phenyl and R³ and R⁴ areeach hydrogen, or R¹ and R³ are each chlorine, bromine, methyl, ethyl,methoxy, phenyl or tert-butyl and R² and R⁴ are each hydrogen, or R¹, R²and R³ are each methyl and R⁴ is hydrogen, or R¹ is methyl, R³ ischlorine or bromine and R² and R⁴ are each hydrogen, or R¹ and R²together form a radical of the formula ##STR18## where z is 1 or 2, andthe fused benzene ring is unsubstituted or monosubstituted ordisubstituted by chlorine, methyl or methoxy, and R³ and R⁴independently of one another are each hydrogen, chlorine or methyl. 9.The radical ion salt as claimed in claim 4, wherein R¹, R², R³ and R⁴are each hydrogen, fluorine, chlorine, methyl or methoxy, or R¹ ischlorine, bromine, methyl, ethyl, methoxy, ethoxy, phenyl or tert-butyland R², R³ and R⁴ are each hydrogen, or R¹ and R⁴ are each chlorine,methyl or methoxy and R² and R³ are each hydrogen, or R¹ and R² are eachchlorine, methyl, methoxy or phenyl and R³ and R⁴ are each hydrogen, orR¹ and R³ are each chlorine, bromine, methyl, ethyl, methoxy, phenyl ortert-butyl and R² and R⁴ are each hydrogen, or R¹, R² and R³ are eachmethyl and R⁴ is hydrogen, or R¹ is methyl, R³ is chlorine or bromineand R² and R⁴ are each hydrogen, or R¹ and R² together form a radical ofthe formula ##STR19## where z is 1 or 2, and the fused benzene ring isunsubstituted or monosubstituted or disubstituted by chlorine, methyl ormethoxy, and R³ and R⁴ independently of one another are each hydrogen,chlorine or methyl.
 10. The radical ion salt as claimed in claim 5,wherein R¹, R², R³ and R⁴ are each hydrogen, fluorine, chlorine, methylor methoxy, or R¹ is chlorine, bromine, methyl, ethyl, methoxy, ethoxy,phenyl or tert-butyl and R², R³ and R⁴ are each hydrogen, or R¹ and R⁴are each chlorine, methyl or methoxy and R² and R³ are each hydrogen, orR¹ and R² are each chlorine, methyl, methoxy or phenyl and R³ and R⁴ areeach hydrogen, or R¹ and R³ are each chlorine, bromine, methyl, ethyl,methoxy, phenyl or tert-butyl and R² and R⁴ are each hydrogen, or R¹, R²and R³ are each methyl and R⁴ is hydrogen, or R¹ is methyl, R³ ischlorine or bromine and R² and R⁴ are each hydrogen, or R¹ and R²together form a radical of the formula ##STR20## where z is 1 or 2, andthe fused benzene ring is unsubstituted or monosubstituted ordisubstituted by chlorine, methyl or methoxy, and R³ and R⁴independently of one another are each hydrogen, chlorine or methyl.